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### Network # DC Gear Motor

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#### Nikyu

Jan 1, 1970
0
I've got a pretty simple question about DC gear motors. I understand
the relationship between torque, motor speed and Hp. Typically when I
see a spec for a motor it list all three values. Are the torque and
speed both attainable at the same time or are those the peak values?
Because when I try to calculate the Hp from the listed torque and
speed, I never the Hp listed.

If I wanted a dc motor to have a torque of 2 ft-lb and a speed of 60
rpm, then the motor would have to be able to put out 0.023 Hp.
Correct?

But as the speed is reduced, the motor can supply much more torque and
like wise as the speed in increased, the motor cannot supply as much
torque.

Is my understanding correct?

Thanks!

J

#### John Popelish

Jan 1, 1970
0
Nikyu said:
I've got a pretty simple question about DC gear motors. I understand
the relationship between torque, motor speed and Hp. Typically when I
see a spec for a motor it list all three values. Are the torque and
speed both attainable at the same time or are those the peak values?
Because when I try to calculate the Hp from the listed torque and
speed, I never the Hp listed.

Often, the HP listed is the motor shaft output, not the gear box output.
If I wanted a dc motor to have a torque of 2 ft-lb and a speed of 60
rpm, then the motor would have to be able to put out 0.023 Hp.
Correct?

Let me check. The torque of 2 ft-lb refers to the ability of the
gearbox to produce a force of 2 pounds at a distance 1 foot from the
axle. But one turn of that axle will pull that 2 pounds through a
distance of 2*pi*1ft=6.28 linear feet. So the work done by the 2
pound force per rotation will be 6.28*2=12.57 ft-lb of work. Multiply
that by 60 rotations per second and you get 754 ft*lb/min or about
..023 of a horse power (1 HP=33,000 ft*lb/min). Check.
But as the speed is reduced, the motor can supply much more torque and
like wise as the speed in increased, the motor cannot supply as much
torque.

Is my understanding correct?

Sounds pretty good to me. A DC (permanent magnet) motor has some zero
load speed at a given supply voltage, and that speed falls pretty
linearly to zero at stall torque. The peak horsepower usually occurs
at about half no load speed (half of stall torque and half of no load
speed).

J

#### Jasen Betts

Jan 1, 1970
0
If I wanted a dc motor to have a torque of 2 ft-lb and a speed of 60
rpm, then the motor would have to be able to put out 0.023 Hp.
Correct?
yes.

But as the speed is reduced, the motor can supply much more torque and
like wise as the speed in increased, the motor cannot supply as much
torque.

yes.

it's probably best to look at the data sheet which will give all the
details, rather than relying a summary from a catalogue.

Bye.
Jasen

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